Nucleic acid vaccine against the sars-cov-2 coronavirus

ABSTRACT

The invention relates to an immunogenic or vaccine composition against the 2019 novel coronavirus (SARS-CoV-2), comprising a nucleic acid construct encoding a SARS-CoV-2 coronavirus Spike (S) protein antigen or a fragment thereof comprising the receptor-binding domain, wherein the nucleic acid construct sequence is codon-optimized for expression in human.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation U.S. application Ser. No. 17/819,187filed on Aug. 11, 2022, which is a continuation of International Appln.PCT/EP2021/025053, filed on Feb. 12, 2021, which itself claims thebenefit of U.S. provisional application 62/976,148 filed on Feb. 13,2020, and European Appln. EP 20305140.4 filed on Feb. 13, 2020, thecontents of each of which are incorporated herein by reference in theirentireties for all purposes.

REFERENCE TO SEQUENCE LISTING SUBMITTED ELECTRONICALLY

The instant application contains a Sequence Listing which has beensubmitted electronically in XML, format and is hereby incorporated byreference in its entirety. Said XML, copy, created on Jul. 12, 2023, isnamed B2006132EPWOUS.xml and is 191,004 bytes in size.

FIELD OF THE INVENTION

The invention relates to an immunogenic or vaccine composition againstthe 2019 novel coronavirus (SARS-CoV-2, 2019-nCov or COVID-19),comprising a nucleic acid construct encoding a SARS-CoV-2 coronavirusSpike (S) protein antigen or a fragment thereof comprising thereceptor-binding domain (RBD), wherein the nucleic acid constructsequence is codon-optimized for expression in human. The invention alsorelates to said nucleic acid construct, derived vector, antigen encodedby said nucleic acid construct and to their use for the diagnosis,prevention and treatment of SARS-CoV-2 coronavirus infection.

BACKGROUND OF THE INVENTION

In December 2019, patients presenting with viral pneumonia were reportedin Wuhan, China. A novel coronavirus was subsequently identified as thecausative agent, and provisionally named 2019 novel coronavirus(2019-nCov or SARS-CoV-2) (Zhu N et al., N Engl J Med., 2020 Jan. 24).The virus swiftly spread within and outside China, leading to the WHOdeclaring a Public Health Emergency of International Concern on Jan. 30,2020. With the aim of rapid development of a candidate vaccine, andbased on the state of the art of betacoronaviruses biology, two suitablecandidate antigens based on the spike (S) protein of the virus weredesigned.

Coronaviruses are enveloped, positive single stranded RNA viruses.Coronaviruses have been identified in various mammalians hosts such asbats, camels, or mice, among others. Several coronaviruses arepathogenic to human, leading to varying degrees of symptoms severity(Cui et al., Nat Rev Microbiol. 2019 March; 17(3):181-92). Highlypathogenic variants include the severe acute respiratory syndromecoronavirus (SARS-Cov) that emerged in China in 2002, resulting in 8000human infections and 700+ deaths (Peiris et al., Nat Med., 2004December; 10(12 Suppl): S88-97) and the Middle East respiratory syndromecoronavirus (MERS-CoV), first detected in Saudi Arabia in 2012 andresponsible for 2500 human infections and 850+ deaths (Zaki et al., NEngl J Med., 2012 Nov. 8; 367(19):1814-20; Lee et al., BMC Infect Dis.2017 Jul. 14; 17(1):498).

Coronaviruses genomes encode non-structural polyprotein and structuralproteins, including the Spike (S), envelope, membrane and nucleocapsidproteins. As seen notably with SARS-Cov, neutralizing antibodies and/orT-cell immune responses can be raised against several proteins butmostly target the S protein, suggesting that S protein-induced specificimmune responses play important parts in the natural response tocoronavirus infection (Saif L J, Vet Microbiol. 1993 November;37(3-4):285-97). The S glycoprotein has key roles in the viral cycle, asit is involved in receptor recognition, virus attachment and entry, andis thus a crucial determinant of host tropism and transmission capacity.Expressed as precursor glycoprotein, S is cleaved in two subunits (S1,which contains the receptor binding domain (RBD), and S2) by proteases.

There is a need for new vaccines to control SARS-CoV-2 virus infection.

SUMMARY OF THE INVENTION

The inventors have engineered a nucleic acid vaccine against the 2019novel coronavirus (SARS-CoV-2 or 2019-nCov) based on its Spike (S)protein coding sequence available in sequence data bases, which has beenoptimized for expression in human. Various nucleic acid constructscontaining either the complete SARS-CoV-2 Spike, a Spike modified at thefurin site), stabilized with proline residues and/or comprising aC-terminal deletion, or only the receptor binding domain (RBD) wereengineered using the optimized Spike coding sequence. To ensure that theantigen will be able to generate a broad immune response that will alsoresult in protection against novel variants of SARS-CoV-2, inventorsincluded point modifications of the antigen in key areas of the spikeand its RBD. This notably involved modifications close to the pocket ofcontact with the receptor ACE2 (region 480-505), as well as regionsalong the spike where changes (mutations or deletion) have been notedduring the natural circulation of the virus in human. Animals werevaccinated with formulation of the various nucleic acid constructs byintramuscular, intranasal, or mixed administration using various primeboost immunization regimens. Nucleic acid vaccine was able to induceneutralizing antibody production. In correlation with strongneutralizing antibody induction, nucleic acid vaccine encoding the RBDantigen was able to provide protection from a SARS-CoV-2 challenge ofimmunized animals, The various derivatives of the initial antigen willbe used in a composition or sequentially in prime boost regimens.

Therefore, the invention relates to an immunogenic or vaccinecomposition against SARS-CoV-2 virus comprising a nucleic acid constructencoding a SARS-CoV-2 virus Spike (S) protein antigen having at least90% identity with the amino acid sequence from positions 19 to 1273 ofSEQ ID NO: 2 or a fragment thereof comprising thereceptor-binding-domain (RBD), wherein the nucleic acid constructsequence is codon-optimized for expression in human.

In some embodiments of the composition according to the invention, thenucleic acid construct comprises a sequence chosen from SEQ ID NO: 1,SEQ ID NO: 3, and the nucleotide sequences having at least 80% identitywith said sequences.

In some preferred embodiments of the composition according to theinvention, said nucleic acid construct comprises a Kozak sequence.

In some preferred embodiments, the nucleic acid construct comprises asequence selected from the group consisting of SEQ ID NO: 10, 12, 14,16, 18, 20, 22, 24, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53,55, 57, 59, 61, 63, 65, the nucleotide sequences having at least 80%identity with said sequences, and the RNA sequences thereof; preferablyselected from the group consisting of SEQ ID NO: 14, 16, 18, 20, 22, 24,31, 33, 35, 37, the nucleotide sequences having at least 80% identitywith said sequences, and the RNA sequences thereof.

In some embodiments of the composition according to the invention, saidRBD fragment comprises an amino acid sequence having at least 90%identity with SEQ ID NO: 4.

In some preferred embodiments of the composition according to theinvention, said S protein antigen or RBD fragment thereof comprises asignal peptide, preferably selected from the group consisting of thesequences SEQ ID NO: 5, 6 and 7.

In some preferred embodiments of the composition according to theinvention, said S protein antigen or RBD fragment thereof furthercomprises at least an epitope recognized by human T cells; preferablyhuman CD4+ T-cells; more preferably a Universal Pan HLA-DR Epitope suchas PADRE (SEQ ID NO: 8); preferably wherein the S protein antigen or RBDfragment thereof and the epitope are separated by a linker, preferablycomprising SEQ ID NO: 9.

In some preferred embodiments of the composition according to theinvention, said S protein antigen or RBD fragment thereof comprises anamino acid sequence selected from the group consisting of SEQ ID NO: 11,13, 15, 17, 19, 21, 23, 25, 30, 32, 34; 36, 38, 40, 42, 44, 46, 48, 50,52, 54, 56, 58, 60, 62, 64, 66 and the sequences having at least 90%identity with said sequences; preferably selected from the groupconsisting of SEQ ID NO: 15, 17, 19, 21, 23, 25, 32, 34, 36, 38, and thesequences having at least 90% identity with said sequences.

In some embodiments of the composition according to the invention, saidnucleic acid construct is a mammalian expression cassette, preferablyhuman expression cassette, wherein the coding sequence of said S proteinantigen or RBD fragment thereof is operably linked to appropriateregulatory sequence(s) for their expression in an individual's targetcells or tissue(s); preferably comprising a promoter; more preferablyfurther comprising one or more of an enhancer, terminator or intron.

In some embodiments of the composition according to the invention, saidnucleic construct is RNA or DNA. In some particular embodiments, the RNAis non-replicating or self-amplifying mRNA comprising a cap structure,5′- and 3′-untranslated regions (UTRs), and a 3′poly(A) tail operablylinked to the coding sequence of said S protein antigen or RBD fragmentthereof.

In some embodiments, the composition according to the inventioncomprises a vector comprising said nucleic acid construct; preferably aviral vector, a plasmid, a nucleic acid delivery agent or combinationthereof. In some particular embodiments, said nucleic acid construct,preferably an expression cassette, is inserted into a viral vector or aplasmid. The viral vector is advantageously selected from the groupconsisting of: cytomegalovirus, adenovirus, vesicular stomatitis virus,modified vaccinia virus ankara and measles virus. In some particularembodiments, the nucleic acid delivery agent comprises tetrafunctionalnon-ionic amphiphilic block copolymers comprising at least onehydrophilic block and at least one hydrophobic block. In some particularembodiments, the plasmid is combined with a nucleic acid delivery agent,preferably comprising tetrafunctional non-ionic amphiphilic blockcopolymers comprising at least one hydrophilic block and at least onehydrophobic block. In some particular embodiments, the nucleic aciddelivery agent comprises a particle or vesicle, in particularlipid-based micro- or nano-vesicle or particle such as liposome or lipidnanoparticle (LNP). In some particular embodiments, the nucleic acidconstruct is RNA, in particular mRNA according to the present disclosureand the vector is a particle or vesicle, in particular LNP.

In some embodiments of the invention, the immunogenic or vaccinecomposition further comprises a pharmaceutically acceptable vehicleand/or an adjuvant.

In some embodiments of the invention, the immunogenic or vaccinecomposition induces humoral and cellular immune responses against saidSARS-CoV-2 virus; preferably wherein the humoral immune responsecomprises neutralizing antibodies against said SARS-CoV-2 virus and/orthe cellular immune response comprises CD4+ and/or CD8+ T-cells againstsaid SARS-CoV-2 virus.

The invention also relates to the immunogenic or vaccine compositionaccording to the present disclosure, for use in the prevention ortreatment of SARS-CoV-2 virus infection.

The invention also relates to the nucleic construct according to thepresent disclosure, the vector comprising said nucleic acid construct,the SARS-CoV-2 virus S protein antigen or fragment thereof comprisingthe receptor binding domain encoded by said nucleic acid construct andto their use for the diagnosis, prevention and treatment of SARS-CoV-2coronavirus infection.

DETAILED DESCRIPTION OF THE INVENTION Nucleic Acid Construct and Vector

The invention relates to a nucleic acid construct encoding a SARS-CoV-2virus Spike (S) protein antigen having at least 90% identity with theamino acid sequence from positions 19 to 1273 of SEQ ID NO: 2 or afragment thereof comprising the receptor-binding-domain, wherein thenucleic acid construct sequence is codon-optimized for expression inhuman.

The nucleic acid construct may consist of recombinant, synthetic orsemi-synthetic nucleic acid which is expressible in the individual'starget cells or tissue. The nucleic acid may be DNA, RNA, mixed and mayfurther be modified. In some embodiments, the nucleic acid constructconsists of recombinant or synthetic DNA or RNA, in particular mRNA. Thenucleic construct has usually a length of up to 10000 nt. Preferably upto 9000, 8000, 7000, 6000 or 5000 nt.

As used herein “individual” or “subject” refers to a human.

The terms “a”, “an”, and “the” include plural referents, unless thecontext clearly indicates otherwise. As such, the term “a” (or “an”),“one or more” or “at least one” can be used interchangeably herein.

As used herein, SARS-CoV-2 refers to any isolate, strain or variant ofSARS-CoV-2.

As used herein, SARS-CoV-2 infection refers to SARS-CoV-2 infection andassociated disease (Covid-19).

The nucleic acid sequences disclosed herein are provided in their DNAform. However, the present invention encompasses the RNA equivalent ofany of the disclosed DNA sequences.

SEQ ID NO: 2 is the amino acid sequence of the Spike (S) protein of the2019 novel coronavirus initially named 2019-nCov and renamed SARS-CoV-2(Severe acute respiratory syndrome coronavirus 2). The S proteincomprises a signal peptide (SP) from position 1 to 18 which is cleavedin the mature S protein. The S protein is cleaved into two subunits, 51which contains the receptor binding domain (RBD) and S2, by proteases.51 is from positions 19 to 661 of SEQ ID NO: 2 and S2 is from positions662 to 1270 of SEQ ID NO: 2 (See FIG. 3 ). The receptor binding domain(RBD) is from positions 331 to 524 in SEQ ID NO: 2 and corresponds toSEQ ID NO: 4 in wild-type SARS-CoV-2. By simple sequence alignment withSEQ ID NO: 2, one skilled in the art can easily determine the positionsof the RBD in the sequence of a S protein antigen variant or fragmentthereof according to the present disclosure. The RBD from wild-typeSARS-CoV-2 S protein or S protein antigen variant or fragment thereofaccording to the present disclosure is highly reactive to anti-Sneutralizing antibodies and competitively inhibits SARS-CoV-2 virusneutralisation by said anti-S neutralizing antibodies. Therefore, the Santigen and the S antigen fragment according to the invention whichcomprises the RBD (RBD fragment, RBD antigen or RBD antigen fragment)are highly reactive to anti-S neutralizing antibodies and competitivelyinhibit SARS-CoV-2 virus neutralisation by said anti-S neutralizingantibodies. This reactivity may be tested by standard antigen/antibodybinding assays such as ELISA and the like or by standard virusneutralisation assay that are well-known in the art such as thosedisclosed in the examples of the application. The amino acid positionsare indicated according to the numbering in the sequence SEQ ID NO: 2.

The S protein antigen or S antigen according to the present disclosurehas at least 90% identity with the amino acid sequence from positions 19to 1273 of SEQ ID NO: 2. In some embodiments, the S antigen has 91%,92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or 100% identity with the aminoacid sequence from positions 19 to 1273 of SEQ ID NO: 2.

In some embodiments, said RBD antigen comprises or consists of an aminoacid sequence having at least 90% identity with SEQ ID NO: 4. The RBDantigen fragment may have 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or100% identity with SEQ ID NO: 4. The RBD antigen fragment according tothe present disclosure refers to a functional fragment which is bound byanti-S neutralizing antibodies in standard antigen/antibody bindingassays such as ELISA and the like and competitively inhibit SARS-CoV-2virus neutralisation by said anti-S neutralizing antibodies in standardvirus neutralization assays. In some preferred embodiments, said RBDantigen fragment consists of the amino acid sequence SEQ ID NO: 4 or asequence having at least 90% identity with SEQ ID NO: 4.

In some particular embodiments, the S antigen or RBD antigen fragmentthereof comprises one or more mutations within the RBD selected from thegroup consisting of: K417N or K417T, N439N, L452R, Y453F, S477N, E484K,F490S, and N501Y, said positions being indicated according to thenumbering in the sequence SEQ ID NO: 2. The S or RBD antigen may have 1,2, 3, 4, 5, 6 or all of said mutations. In some particular embodiments,the S or RBD antigen comprises at least one mutation close to the pocketof contact with the receptor ACE2 (region 480-505) chosen from E484K,F490S, and N501Y; preferably at least the E484K and/or N501Y mutations.

In some preferred embodiments, the S or RBD antigen comprises thefollowing mutations: N501Y; E484K and N501Y; K417T or K417N, E484K andN501Y; K417N, N439N, Y453F, S477N, E484K, F490S, and N501Y; K417N,N439N, L452R, S477N, E484K, F490S, and N501Y. In some more preferredembodiment, the S antigen comprises or consists of an amino acidsequence having at least 90% identity with any one of SEQ ID NO: 44, 46,48, 50, 52, 54, 56, 58, 60, 62, 64 and 66, wherein said variantcomprises one or more of said mutations within the RBD domain. In somemore preferred embodiment, the RBD antigen comprises or consists of anamino acid sequence having at least 90% identity with any one of SEQ IDNO: 32, 34, 36 and 38, wherein said variant comprises one or more ofsaid mutations within the RBD domain.

In some particular embodiments, the S antigen comprises a mutation whichinactivates the furin cleavage site (PRRAR; positions 681 to 685 in SEQID NO: 2). Examples of such furin site mutation, including deletion orsubstitution are well-known in the art and include the deletion ofresidues P681 to A684 (Johnson et al., Nature, 2021,doi.org/10.1038/s41586-021-03237-4) and the R682G, R683S and/or R685Ssubstitutions. In some preferred embodiments, the S antigen comprisesthe R682G, R683S and R685S substitutions. In some more preferredembodiment, the S antigen comprises or consists of an amino acidsequence having at least 90% identity with SEQ ID NO: 30, wherein thevariant comprises said furin site mutation.

In some particular embodiments, the S antigen comprises a mutation whichstabilizes the Spike trimer. Such mutations which are well-known in theart include the K986P and V987P mutations (S-2P variant) and otherproline substitutions, in particular F817P, A892P, A899P and A942P,which can be combined together to obtain a multiple proline variant, inparticular hexaproline variant (HexaPro). In some preferred embodiments,the S antigen comprises the K986P and V987P mutations, and eventuallyone to four additional proline mutations selected from the groupconsisting of F817P, A892P, A899P and A942P. In some more preferredembodiment, the S antigen comprises or consists of an amino acidsequence having at least 90% identity with any one of SEQ ID NO: 42, 48,50, 56, 58, 64 and 66, wherein the variant comprises at least one ofsaid Proline mutations.

In some particular embodiments, the S antigen comprises a C-terminaldeletion of 1 to 25 or more amino acids, preferably 5 to 25, 10 to 25amino acids; more preferably 18 to 25 amino acids (18, 19, 20, 21, 22,23, 24, 25). In some preferred embodiments, the S antigen comprises thedeletion of the C-terminal residues from position K1255 (deletion K1255to T1273). In some more preferred embodiment, the S antigen comprises orconsists of an amino acid sequence having at least 90% identity with anyone of SEQ ID NO: 40, 46, 50, 54, 58, 62 and 66, wherein the variantcomprises said C-terminal deletion.

In some particular embodiments, the S antigen comprises one or moremutations selected from the group consisting of: the substitutions L18F,T20N, P26S, D80A, D138Y, R190S, D215G, A570D, D614G, H655Y, P681H,A701V, T716I, S982A, T1027I, D1118H and V1176F; and the deletions delta69-70, delta 144 and delta 242-244. In some preferred embodiments, the Santigen comprises at least five of said substitutions outside the RBD,and eventually also at least one or two of said deletions. In some morepreferred embodiment, the S antigen comprises or consists of an aminoacid sequence having at least 90% identity with any one of SEQ ID NO:44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64 and 66, wherein said variantcomprises one or more of said mutations outside the RBD domain.

The percent amino acid or nucleotide sequence identity is defined as thepercent of amino acid residues or nucleotides in a Compared Sequencethat are identical to the Reference Sequence after aligning thesequences and introducing gaps if necessary, to achieve the maximumsequence identity and not considering any conservative substitution aspart of the sequence identity. Sequence identity is calculated over theentire length of the Reference Sequence. Alignment for purposes ofdetermining percent amino acid or nucleotide sequence identity can beachieved in various ways known to a person of skill in the art, forinstance using publicly available computer software such as the GCG(Genetics Computer Group, Program Manual for the GCG Package, Version 7,Madison, Wisconsin) pileup program, or any of sequence comparisonalgorithms such as BLAST (Altschul et al., J. Mol. Biol., 1990, 215,403-10), FASTA or CLUSTALW.

The nucleic acid construct sequence is codon-optimized for expression inhuman. Codon optimization is used to improve protein expression level inliving organism by increasing translational efficiency of target gene.Appropriate methods and softwares for codon optimization in the desiredhost are well-known in the art and publically available (see for examplethe GeneOptimizer software suite in Raab et al., Systems and SyntheticBiology, 2010, 4, (3), 215-225). Codon optimization of the nucleic acidconstruct sequence relates to the coding sequences but not to the other(non-coding) sequences of the nucleic acid construct.

In some embodiments, the nucleic acid construct comprises a sequencechosen from SEQ ID NO: 1 and SEQ ID NO: 3, the nucleotide sequenceshaving at least 80% identity with said sequences, and the RNA sequencesthereof. The nucleotide sequences may have 81%, 82%, 83%, 84%, 84%, 85%,86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or100% identity with SEQ ID NO: 1 or SEQ ID NO: 3.

In some preferred embodiments, the nucleic acid construct comprises aKozak consensus sequence or Kozak sequence which is a nucleic acid motifthat functions as the protein translation initiation site in mosteukaryotic mRNA transcripts. The Kozak sequence may be acc (in position−3 to −1) or cacc (in positions −4 to −1) relative to the atg initiationcodon of the S protein antigen or antigen fragment.

In some preferred embodiments, the nucleic acid construct comprises asequence selected from the group consisting of SEQ ID NO: 10, 12, 14,16, 18, 20, 22, 24, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53,55, 57, 59, 61, 63, 65, and the nucleotide sequences having at least 80%identity with said sequences, and the RNA equivalent thereof. Thenucleotide sequences may have 81%, 82%, 83%, 84%, 84%, 85%, 86%, 87%,88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or 100%identity with any one of SEQ ID NO: 10, 12, 14, 16, 18, 20, 22, 24, 29,31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63 or65. In some more preferred embodiments, the nucleic acid constructcomprises a sequence selected from the group consisting of SEQ ID NO:14, 16, 18, 20, 22, 24, 31, 33, 35, 37, the nucleotide sequences havingat least 80% identity with said sequences, and the RNA sequencesthereof. All the above listed sequences are codon-optimized forexpression in human and comprise a Kozak sequence. The above listedvariants of the listed sequences refer to sequences that arecodon-optimized for expression in human and preferably comprising aKozak sequence.

In some preferred embodiments, said S protein antigen or RBD fragmentthereof comprises a signal peptide (SP) or signal sequence. The SP is atthe amino terminus of a protein and is involved in transport of theprotein to or through cell membranes, transport to different membranouscellular compartments, or secretion of the protein from the cell. Signalpeptides are removed from the mature protein during this process by aspecific peptidase. For example, the signal peptide may be the naturalSP of the S protein (SEQ ID NO: 5) or the SP of a human protein such asCD5 (SEQ ID NO: 6) or IL2 (SEQ ID NO: 7). In some more preferredembodiments, the signal peptide is selected from the group consisting ofthe sequences SEQ ID NO: 5, 6 and 7 and the derived sequences having aC-ter deletion of 1, 2, 3 or 4 amino acids. In some embodiments, the SPof the human protein further comprises the 1 to 4 amino acid residues inpositions +1 to +4 relative to the peptidase cleavage site in said humanprotein. In some embodiments, the SP of the SARS-CoV-2 S protein antigen(SEQ ID NO: 5) further comprises 1, 2, 3 or 4 amino acid residues at itsCter, preferably comprising V and/or A or is truncated from 1, 2, 3 or 4amino acid residues at its Cter.

In some preferred embodiments, the S protein antigen or RBD fragmentthereof further comprises at least an epitope recognized by human Tcells; preferably human CD4+ T-cells; more preferably a Universal PanHLA-DR Epitope such as PADRE. PADRE is a universal synthetic 13 aminoacid peptide (SEQ ID NO: 8) that activates CD4+ T cells. As PADRE bindswith high affinity to 15 of the 16 most common human HLA-DR types, itprovides potent CD4+ T cell responses, and may overcome problems causedby polymorphism of HLA-DR molecules in human populations. The S proteinantigen or fragment thereof and the epitope are advantageously separatedby a linker, such as for example preferably a linker comprising orconsisting of SEQ ID NO: 9. In some more preferred embodiments, the Sprotein antigen or fragment thereof comprises PADRE (SEQ ID NO: 8) andpreferably further comprises the linker of SEQ ID NO: 9, correspondingto SEQ ID NO: 27. The linker and PADRE sequences are advantageouslyencoded by the nucleotide sequence SEQ ID NO: 26.

The S antigen and its fragment according to the present disclosureusually do not comprise any other protein moiety or domain other thanthose disclosed above. In particular, the S antigen and its fragmentaccording to the present disclosure differ from the prior art antigensin that they do not comprise a protein stabilizing moiety such as animmunoglobulin Fc fragment.

In some preferred embodiments, said S protein antigen or RBD fragmentthereof comprises an amino acid sequence selected from the groupconsisting of the sequences SEQ ID NO: 11, 13, 17, 19, 21, 23, 25, 30,32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66and the variant thereof having at least 90% identity (91%, 92%, 93%,94%, 95%, 96%, 97%, 98%, 99% or 100% identity) with one of saidsequences. SEQ ID NO: 11, 13, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58,60, 62, 64, 66 comprise the full length S protein (Spike) sequenceincluding the natural SP. SEQ ID NO: 30 comprises a spike modified atthe furin site (spike delta furin). SEQ ID NO: 17, 25, 32, 34, 36 and 38comprise the RBD with the natural SP at the N-terminus. SEQ ID NO: 19,21, 23, 25 comprise the RBD with another SP at the N-terminus (SEQ IDNO: 6 or 7). SEQ ID NO: 13, 17, 21 and 25 comprise the linker (SEQ IDNO: 9) and PADRE at the C-terminus (SEQ ID NO: 27).

In some more preferred embodiments, the nucleic acid construct encodes aRBD fragment having a sequence selected from the group consisting of thesequences SEQ ID NO: 15, 17, 19, 21, 23, 25, 32, 34, 36, 38 and thevariant thereof having at least 90% identity (91%, 92%, 93%, 94%, 95%,96%, 97%, 98%, 99% or 100% identity) with one of said sequences.

A variant according to the present disclosure refers to a functionalvariant which is bound by anti-S neutralizing antibodies in standardantigen/antibody binding assays such as ELISA and the like andcompetitively inhibit SARS-CoV-2 virus neutralisation by said anti-Sneutralizing antibodies in standard virus neutralization assays

In some embodiments, said nucleic acid construct is a mammalianexpression cassette, preferably human expression cassette, wherein thecoding sequence of said S protein antigen or RBD fragment thereof isoperably linked to appropriate regulatory sequence(s) for theirexpression in an individual's target cells or tissue(s). In someparticular embodiments, the target cell(s) or tissue(s) is epithelialcell(s) or tissue(s). Such sequences which are well-known in the artinclude in particular a promoter, and further regulatory sequencescapable of further controlling the expression of a transgene, such aswithout limitation, enhancer, terminator and intron. In some particularembodiments, the expression cassette comprises a promoter; preferablyfurther comprises one or more of an enhancer, terminator or intron.

The promoter may be a tissue-specific, ubiquitous, constitutive orinducible promoter that is functional in the individual's target cellsor tissue, in particular epithelial cell(s) or tissue(s). Examples ofconstitutive promoters which can be used in the present inventioninclude without limitation: phosphoglycerate kinase promoter (PGK),elongation factor-1 alpha (EF-1 alpha) promoter including the short formof said promoter (EFS), viral promoters such as cytomegalovirus (CMV)immediate early enhancer and promoter (optionally with the CMVenhancer), cytomegalovirus enhancer/chicken beta actin (CAG) promoter,SV40 early promoter and retroviral 5′ and 3′ LTR promoters includinghybrid LTR promoters. Preferred ubiquitous promoter is CMV promoter.Examples of inducible promoters which can be used in the presentinvention include Tetracycline-regulated promoters. The promoters areadvantageously human promoters, i.e., promoters from human cells orhuman viruses. Such promoters are well-known in the art and theirsequences are available in public sequence data bases.

In some embodiments, the nucleic acid construct encodes otherantigen(s), in particular human vaccine antigen(s) from other pathogens.

In some preferred embodiments, the nucleic acid construct is DNA,wherein the coding sequence of said S protein antigen or RBD fragmentthereof is operably linked to appropriate regulatory sequence(s) fortheir expression in an individual's target cells or tissue(s) asdisclosed above. The DNA construct advantageously comprises a mammalianexpression cassette as disclosed above.

In some other preferred embodiments, the nucleic acid construct is RNA,preferably mRNA, wherein the coding sequence of said S protein antigenor RBD fragment thereof is operably linked to appropriate regulatorysequence(s) for their expression in an individual's target cells ortissue(s). mRNA vaccines are well-known in the art (reviewed in Jacksonet al., Vaccines, 2020, 5, 11, doi.10.1038). mRNA is delivered into thehost cell cytoplasm where expression generates the antigen of interest.mRNA construct comprises a cap structure, 5′ and 3′untranslated regions(UTRs), and open reading frame (ORF), and a 3′poly(A) tail. mRNAconstruct may be non-replicating mRNA (MRM) or self-amplifying mRNA(SAM). SAM comprises the inclusion of genetic replication machineryderived from positive-strand mRNA viruses, most commonly alphavirusessuch as Sindbis and Semliki-Forest viruses. In SAM constructs, the ORFencoding viral structural protein is replaced by the transcript encodingthe vaccine antigen of interest, and the viral RNA-dependent RNApolymerase is retained to direct cytoplasmic amplification of thereplicon construct. Trans-replicating RNA are disclosed for example inWO 2017/162461. RNA replicon from alphavirus suitable for geneexpression are disclosed in WO 2017/162460. mRNA manufacturing processuses plasmid DNA (pDNA) containing a DNA-dependent RNA polymerasepromoter, such as T7, and the corresponding sequence for the mRNAconstruct. The pDNA is linearized to serve as a template for theDNA-dependent RNA polymerase to transcribe the mRNA, and subsequentlydegraded by a DNase process step. The addition of the 5′ cap and the3′poly(A) tail can be achieved during the in vitro transcription step orenzymatically after transcription. Enzymatic addition of the cap can beaccomplished by using guanylyl transferase and 2′-O-methyltransferase toyield a Cap0(^(N7Me)GpppN) or Cap1 (N^(7Me)GpppN^(2′-oMe)) structure,respectively, while the poly-A tail can be achieved through enzymaticaddition via poly-A polymerase. mRNA is then purified using standardmethods suitable for mRNA purification such as high-pressure liquidchromatography (HPLC) and others. Methods for producing mRNA aredisclosed for example in WO 2017/182524.

To improve translation efficiency in vaccinated subject cells, the mRNAconstruct according to the invention comprises a sequence which iscodon-optimized for expression in human. Further improvements of themRNA construct according to the invention to improve its stability andtranslation efficiency in vivo include optimization the length andregulatory element sequences of 5′-UTR and 3′UTR; base and/or sugarmodifications in the cap structure to increase ribosomal interactionand/or mRNA stability; and modified nucleosides. Modified nucleosidesmay be in the 5′-UTR, 3′-UTR or ORF. Examples of modified nucleosidesinclude pseudouridine and N-1-methylpseudouridine that removeintracellular signalling triggers for protein kinase R activation.Examples of modified nucleosides that reduce RNA degradation into cellsare disclosed in WO 2013/039857. Modified cap structures are disclosedin WO 2011/015347 and WO 2019/175356. Optimized 3′-UTR sequences aredisclosed in WO 2017/059902. Modified polyA sequences which improve RNAstability and translation efficiency are disclosed in US 2020/0392518.Modified mRNA with improved stability and translation efficiency arealso disclosed in WO 2007/036366.

The invention also relates to a vector comprising the nucleic acidconstruct according to the present disclosure. The invention may use anyvector suitable for the delivery and expression of nucleic acid intoindividual's cells, in particular suitable for vaccination. Such vectorsthat are well-known in the art include viral and non-viral vectors.

Non-viral vector includes the various (non-viral) agents which arecommonly used to either introduce or maintain nucleic acid intoindividual's cells. Agents which are used to introduce nucleic acid intoindividual's cells by various means include in particular polymer-based,particle-based, lipid-based, peptide-based delivery vehicles orcombinations thereof, such as with no limitations cationic polymer,dendrimer, micelle, liposome, lipopolyplex, exosome, microparticle andnanoparticle including lipid nanoparticle (LNP) and viral-likeparticles; and cell penetrating peptides (CPP).

In some embodiments, said nucleic-acid delivery agent comprisestetrafunctional non-ionic amphiphilic block copolymers comprising atleast one hydrophilic block and at least one hydrophobic block. Suchagents are disclosed in WO 2019/092002.

Agents which are used to maintain nucleic acid into individual's cellsinclude in particular naked nucleic acid vectors such as plasmids,transposons and mini-circles. These vectors have minimal eukaryoticsequences to minimize the possibility of chromosomal integration.Examples of such vectors are the plasmids pVAX1 and pGWIS which arecommercially available. In addition, these approaches can advantageouslybe combined to introduce and maintain the nucleic acid of the inventioninto individual's cells.

In some embodiments, a plasmid, preferably with minimal eukaryoticsequences, comprising an expression cassette including the nucleic acidconstruct according to the present disclosure is combined with anucleic-acid delivery agent, preferably an agent comprisingtetrafunctional non-ionic amphiphilic block copolymers comprising atleast one hydrophilic block and at least one hydrophobic block asdisclosed above.

In some embodiments, a mRNA construct according to the present inventionas disclosed above is combined with a nucleic-acid delivery agentsuitable for delivery of mRNA into mammalian host cells that arewell-known in the art. The mRNA delivery agent may be a polymericcarrier, polycationic protein or peptide, lipid nanoparticle or other.For example, the mRNA (non-replicating or self-amplifying) may bedelivered into cells using polymers, in particular cationic polymers,such as polyethylenimine (PEI), poly-L-Lysin (PEL), polyvinylamine (PVA)or polyallylamine (PAA), wherein the mRNA is preferentially present inthe form of monomers, dimers, trimers or oligomers as disclosed in WO2021/001417. Alternatively, the mRNA may be combined withpolyalkyleneimine in the form of polyplex particles, suitable forintramuscular administration as disclosed in WO 2019/137999 or WO2018/011406. The mRNA may also be combined with a polycation, inparticular protamine, as disclosed in WO 2016/000792. One or more mRNAmolecules may be formulated within a cationic lipid nanoparticle (LNP);for example the formulation may comprise 20-60% cationic lipid; 5-25%non-cationic lipid, 25-55% sterol and 0.5-15% PEG-modified lipid asdisclosed WO 2015/164674. The mRNA may also be formulated in RNAdecorated particles such as RNA decorated lipid particles, preferablyRNA decorated liposomes as disclosed in WO 2015/043613.

Viral vectors are by nature capable of penetrating into cells anddelivering nucleic acid(s) of interest into cells, according to aprocess named as viral transduction. As used herein, the term “viralvector” refers to a non-replicating, non-pathogenic virus engineered forthe delivery of genetic material into cells. In viral vectors, viralgenes essential for replication and virulence are replaced with anexpression cassette for the transgene of interest. Thus, the viralvector genome comprises the transgene expression cassette flanked by theviral sequences required for viral vector production. As used herein,the term “recombinant virus” refers to a virus, in particular a viralvector, produced by standard recombinant DNA technology techniques thatare known in the art. As used herein, the term “virus particle” or“viral particle” is intended to mean the extracellular form of anon-pathogenic virus, in particular a viral vector, composed of geneticmaterial made from either DNA or RNA surrounded by a protein coat,called the capsid, and in some cases an envelope derived from portionsof host cell membranes and including viral glycoproteins. As usedherein, a viral vector refers to a viral vector particle.

A preferred viral vector for delivering the nucleic acid of theinvention is a vaccine vector, preferably selected from the groupconsisting of poxvirus such as vaccinia virus, replication-defectivealphavirus replicons, cytomegalovirus, adenovirus, modified vacciniavirus Ankara, vesicular stomatitis virus and measles virus (For areview, see Humphreys et al., Immunology, 2017, 153, 1-9). In someparticular embodiment, the viral vector is selected from the groupconsisting of: cytomegalovirus, adenovirus, modified vaccinia virusAnkara, vesicular stomatitis virus and measles virus.

In particular embodiments, the vector is a particle or vesicle, inparticular lipid-based micro- or nano-vesicle or particle such asliposome or lipid nanoparticle (LNP). In more particular embodiments,the nucleic acid is RNA, in particular mRNA and the vector is a particleor vesicle, in particular LNP as described above. The LNP: mRNA massratio can be around 10:1 to 30:1.

In some embodiments, vector comprises another nucleic acid constructcoding another antigen, in particular human vaccine antigen(s) fromother pathogens.

The nucleic acid construct, preferably comprising an expressioncassette, is useful for producing recombinant SARS-CoV-2 virus S proteinantigen and fragment thereof comprising the receptor-binding domain(RBD) according to the present disclosure by expression from anappropriate recombinant expression vector in a suitable cell system(eukaryotic including mammalian and insect cells or prokaryotic). Forexample, the vector may be a plasmid in mammalian cells or a baculovirusvector in insect cells.

Therefore, the invention also relates to a host cell (eukaryotic orprokaryotic) modified with a recombinant vector comprising the nucleicacid construct according to the present disclosure.

Immunogenic or Vaccine Composition and Therapeutic Use

The invention further provides an immunogenic or vaccine compositioncomprising a comprising a nucleic acid construct or vector according tothe present disclosure.

The immunogenic or vaccine composition may comprise a mixture ofdifferent nucleic acid constructs or vectors according to the presentinvention. In particular, the composition may comprise a mixture ofnucleic acid constructs or vectors encoding variants of the S antigenand/or RBD antigen as described herein. In some embodiments, thecomposition encodes at least two S and/or RBD antigens having differentmutations within the RBD sequence and/or outside the RBD sequence asdescribed herein. In some preferred embodiments, the pharmaceuticalcomposition encodes at least two, three or four different RBD antigensselected from the group consisting of the sequences SEQ ID NO: 15, 32,34, 36 and 38.

In some embodiments, the pharmaceutical composition further comprises apharmaceutically acceptable vehicle and/or an adjuvant.

The pharmaceutical vehicles are those appropriate to the planned routeof administration, which are well known in the art.

Non-limitative examples of adjuvants suitable for use in the compositionof the invention include: CpG oligodeoxynucleotide, polyI:C(polyinosinc-polycytidylic acid), oil emulsion, mineral substances,bacterial extracts, saponin, aluminium salts, monophosphoryl-lipid A(MPL) and squalene.

The pharmaceutical composition comprises a therapeutically effectiveamount of the nucleic acid construct or vector sufficient to induce animmune response, in particular a protective immune response againstSARS-CoV-2 virus infection, in the individual to whom it isadministered. The pharmaceutically effective dose depends upon thecomposition used, the route of administration, the physicalcharacteristics of the specific individual under consideration,concurrent medication, and other factors, that those skilled in themedical arts will recognize.

The pharmaceutical composition of the present invention is generallyadministered according to known procedures, at dosages and for periodsof time effective to induce a beneficial effect in the individual. Theadministration may be by injection or by mucosal administration, inparticular intranasal administration, or mixed administration. Forexample, the administration may be by intramuscular, intradermal,intravenous or subcutaneous injection, transdermal (such as patch) orintranasal (such as spray) applications, oral, or mixed. In someembodiments, the administration is intramuscular, intranasal or mixedintranasal and intramuscular. The pharmaceutical composition maycomprise between 10 ng and 10 mg of nucleic acid construct or vector ofthe invention; preferably between 100 ng and 2.5 mg, more preferablybetween 1 μg and 500 μg. The pharmaceutical composition is administered1 to 3 times at intervals of 2 to 25 weeks. In some embodiments, thepharmaceutical composition is administered according to a prime-boostregimen comprising 2 or 3 administrations in total, preferablyintramuscular, intranasal or mixed. In some preferred embodiments theprime-boost regimen comprises 2 administrations at interval of at least3 weeks, preferably 3, 4, 5 or 6 weeks. In some other preferredembodiments the prime-boost regimen comprises 3 administrations atintervals of up to 3 weeks, preferably 1 or 2 weeks.

In some embodiments, several pharmaceutical compositions, comprisingdifferent nucleic acid constructs or vectors according to the presentinvention are administered separately or sequentially. In particular,several pharmaceutical compositions encoding different variants of the Santigen and/or RBD fragment thereof are administered separately orsequentially. In some embodiments, the pharmaceutical compositions alltogether encode at least two different RBD antigens selected from thegroup consisting of the sequences SEQ ID NO: 15, 32, 34, 36 and 38.

In some embodiments of the invention, the immunogenic or vaccinecomposition induces humoral and cellular immune responses against saidSARS-CoV-2 virus; preferably wherein the humoral immune responsecomprises neutralizing antibodies against said SARS-CoV-2 virus, inparticular SARS-CoV-2 and/or the cellular immune response comprises CD4+and/or CD8+ T-cells against said SARS-CoV-2 virus.

The invention also relates to the immunogenic or vaccine compositionaccording to the present disclosure, for use in the prevention ortreatment of SARS-CoV-2 virus infection.

The invention provides also a method for preventing SARS-CoV-2 virusinfection in an individual, comprising: administering a therapeuticallyeffective amount of the pharmaceutical composition according to theinvention to the individual.

Antigen, Diagnostic and Therapeutic Uses

The invention also relates to the SARS-CoV-2 virus S protein antigen orfragment thereof comprising the receptor binding domain according to thepresent disclosure.

The SARS-CoV-2 virus Spike (S) protein antigen has at least 90% identitywith the amino acid sequence from positions 19 to 1273 of SEQ ID NO: 2.The S antigen fragment comprises an amino acid sequence having at least90% identity with SEQ ID NO: 4.

In some preferred embodiments, said S protein antigen or fragmentthereof comprises a signal peptide (SP) or signal sequence. The SP is atthe amino terminus of a protein and is involved in transport of theprotein to or through cell membranes, transport to different membranouscellular compartments, or secretion of the protein from the cell. Signalpeptides are removed from the mature protein during this process by aspecific peptidase. For example, the signal peptide may be the naturalSP of the S protein (SEQ ID NO: 5) or the SP of a human protein such asCD5 (SEQ ID NO: 6) or IL2 (SEQ ID NO: 7). In some more preferredembodiments, the signal peptide is selected from the group consisting ofthe sequences SEQ ID NO: 5, 6 and 7.

In some preferred embodiments, the S protein antigen or fragment thereoffurther comprises at least an epitope recognized by human T cells;preferably human CD4+ T-cells; more preferably a Universal Pan HLA-DREpitope such as PADRE. PADRE is a universal synthetic 13 amino acidpeptide (SEQ ID NO: 8) that activates CD4+ T cells. As PADRE binds withhigh affinity to 15 of the 16 most common human HLA-DR types, itprovides potent CD4+ T cell responses, and may overcome problems causedby polymorphism of HLA-DR molecules in human populations. The S proteinantigen or fragment thereof and the epitope are advantageously separatedby a linker, such as for example preferably a linker comprising orconsisting of SEQ ID NO: 9. In some more preferred embodiments, the Sprotein antigen or fragment thereof comprises PADRE (SEQ ID NO: 8) andpreferably further comprises the linker of SEQ ID NO: 9, correspondingto SEQ ID NO: 27.

The S antigen and its fragment according to the present disclosureusually do not comprise any other protein moiety or domain other thanthose disclosed above. In particular, the S antigen and its fragmentaccording to the present disclosure differ from the prior art antigensin that they do not comprise a protein stabilizing moiety such as animmunoglobulin Fc fragment.

In some preferred embodiments, said S protein antigen or fragmentthereof comprises an amino acid sequence selected from the groupconsisting of the sequences SEQ ID NO: 11, 13, 15, 17, 19, 21, 23, 25,30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64,66, and the variant thereof having at least 90% identity (91%, 92%, 93%,94%, 95%, 96%, 97%, 98%, 99% or 100% identity) with one of saidsequences. SEQ ID NO: 11, 13, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58,60, 62, 64, 66 comprise the full length S protein sequence including thenatural SP. SEQ ID NO: 30 comprises a spike modified at the furin site(spike delta furin). SEQ ID NO: 15, 17, 25, 32, 34, 36 and 38 comprisethe RBD with the natural SP at the N-terminus. SEQ ID NO: 19, 21, 23, 25comprise the RBD with another SP at the N-terminus (SEQ ID NO: 6 or 7).SEQ ID NO: 13, 17, 21 and 25 comprise the linker (SEQ ID NO: 9) andPADRE at the C-terminus (SEQ ID NO: 27). A variant according to thepresent disclosure refers to a functional variant which is bound byanti-S neutralizing antibodies in standard antigen/antibody bindingassays such as ELISA and the like.

The SARS-CoV-2 virus S protein antigen and fragment thereof comprisingthe receptor binding domain according to the present disclosure areuseful as reagent for the detection or diagnosis of SARS-CoV-2 virus.

In some aspects, the method of detection or diagnosis of SARS-CoV-2virus comprises determining the presence of antibodies against saidvirus or thereto in a sample.

The detection or diagnosis is generally performed by immunoassay.Immunoassays are well-known techniques for antibody detection which relyon the detection of antigen-antibody complexes using an appropriatelabel. The method of the invention may use any immunoassay such as withno limitations, immunoblotting, immunoprecipitation, ELISA,immunocytochemistry or immunohistochemistry, and immunofluorescence likeflow cytometry assay, and FACS. The method of the invention may use anyappropriate label used in immunoassays such as enzymes, biotin,fluorescent dyes/proteins or others.

In some embodiments, the method of detection or diagnosis of SARS-CoV-2virus infection comprises the step of:

-   -   incubating the SARS-CoV-2 virus S protein antigen or fragment        thereof comprising the receptor binding domain according to the        present disclosure with the biological sample to form a mixture;        and    -   detecting antigen-antibody complexes in the mixture.

The sample for anti-SARS-CoV-2 virus antibody detection is preferablybody fluid from the individual, in particular serum.

The antigen is preferably labeled and the antigen-antibody complexes aredetected by measuring the signal from the label by any appropriate meansavailable for that purpose as disclosed above.

In some embodiments, the detecting step comprises the determination ofthe amount of bound antibody in the mixture, and optionally, comparingthe amount of bound antibody in the mixture with at least onepredetermined value.

The detection of the antibody in a sample from the individual using themethods of the invention is indicative of whether the individual issuffering from SARS-CoV-2 virus past or present infection.

Therefore, the above methods of the invention are useful for thediagnosis of SARS-CoV-2 virus infection in an individual, in particularthe diagnosis of the disease caused by SARS-CoV-2 virus, ranging fromfebrile illness to severe acute respiratory syndrome.

In some embodiments, the above methods comprise the step of deducingtherefrom whether the individual is suffering from SARS-CoV-2 virusinfection i and in particular from a disease caused by SARS-CoV-2 virus.

In some embodiments in connection with this aspect of the invention, theabove methods comprise a further step of administering an appropriatetreatment to the individual depending on whether or not the individualis diagnosed with SARS-CoV-2 virus virus infection and in particularwith a disease caused by SARS-CoV-2 virus.

Another aspect of the invention is a kit for the diagnosis or detectionof SARS-CoV-2 virus, comprising at least one antigen for the detectionof SARS-CoV-2 virus antibody, as defined above, preferably furtherincluding a detectable label.

Another aspect of the invention, relates to an immunogenic or vaccinepharmaceutical composition comprising, as active substance a SARS-CoV-2virus S protein antigen or a fragment thereof comprising the receptorbinding domain according to the present disclosure, in association withat least one pharmaceutically acceptable vehicle.

The pharmaceutical vehicles are those appropriate to the planned routeof administration, which are well known in the art.

The pharmaceutical composition may further comprise a carrier and/oradjuvant. Non-limitative examples of carriers suitable for use in thecomposition of the invention include uni- or multi-lamellar liposomes,ISCOMS, virosomes, viral pseudo-particules, saponin micelles, saccharid(poly(lactide-co-glycolide)) or gold microspheres, and nanoparticules.Non-limitative examples of adjuvants suitable for use in the compositionof the invention include: CpG oligodeoxynucleotide, polyI:C(polyinosinc-polycytidylic acid), oil emulsion, mineral substances,bacterial extracts, saponin, aluminium salts, monophosphoryl-lipid A andsqualene.

The pharmaceutical composition comprises a therapeutically effectiveamount of the antigen sufficient to induce a protective immune responseagainst SARS-CoV-2 virus infection in the individual to whom it isadministered. The pharmaceutically effective dose depends upon thecomposition used, the route of administration, the physicalcharacteristics of the specific human under consideration, concurrentmedication, and other factors, that those skilled in the medical artswill recognize.

The invention provides also a SARS-CoV-2 virus S protein antigen or afragment thereof comprising the receptor binding domain according to thepresent disclosure for use as a medicament.

The invention provides also a SARS-CoV-2 virus S protein antigen or afragment thereof comprising the receptor binding domain according to thepresent disclosure or pharmaceutical composition according to theinvention for use in the prevention or treatment of SARS-CoV-2 virusinfection and associated disease.

The invention provides also a method for preventing or treatingSARS-CoV-2 virus infection and associated disease, comprising:administering a therapeutically effective amount of the pharmaceuticalcomposition according to the invention to the individual.

The pharmaceutical composition of the present invention is generallyadministered according to known procedures, at dosages and for periodsof time effective to induce a beneficial effect in the individual. Theadministration may be by injection or mucosal administration, inparticular respiratory such as intranasal administration.

The practice of the present invention will employ, unless otherwiseindicated, conventional techniques which are within the skill of theart. Such techniques are explained fully in the literature.

The invention will now be exemplified with the following examples, whichare not limitative, with reference to the attached drawings in which:

FIGURE LEGENDS

FIG. 1 . Phylogenetic analysis of representative Betacoronaviruses andSARS-CoV-2 based on full length genome sequences.

The tree is midpoint rooted for ease of visualization, and highbootstrap values are indicated at key nodes.

FIG. 2A-B. Homology modelling of the S protein of SARS-CoV-2 using theSwiss-Model tool (FIG. 2A) and showing the model based on the top-hit(PDB ID: 6ACD) (FIG. 4C B).

The putative RBD is highlighted with a black box in the alignment. TheQMEAN score reflects the modelling quality. Similar results wereobtained using Phyre2.

FIG. 3 . Schematic representation of the selected antigens.

SP: Signal Peptide. RBD: Receptor Binding Domain.

FIG. 4A-C. SARS-CoV-2 neutralizing antibody titers in immunized BALB/cmice.

FIG. 4A Immunization scheme. Groups of 5 female Balb/c mice wereimmunized intra muscularly with 100 pg of pVAX vector containing thesequence of either the SARS-CoV-2 spike (pVAX-Spike), the spike with amutated furin cleavage site (pVAX-Spike-deltaFurin), the receptorbinding domain with the signal peptide of the spike (pVAX-RBD), the sameRBD antigen with the PADRE sequence in 3′ (pVAX-RBD-PADRE), or an emptyvector (pVAX).

FIG. 4B Neutralizing antibody titers against SARS-CoV-2 at day 27 postimmunization (prime), determined by plaque reduction neutralizing test(PRNT₅₀).

FIG. 4C Neutralizing antibody titers against SARS-CoV-2 at day 47 postimmunization (prime-boost), determined by PRNT₅₀.

FIG. 5A-D. Immunogenicity and protective efficacy.

Groups of 5-8 female Balb/c mice were immunized intra muscularly (i.m.)with 100 μg of pVAX vector containing the sequence of the spike receptorbinding domain with the signal peptide of the spike (pVAX-RBD) or anempty vector (pVAX). The immunization route was either i.m., intra nasal(i.n.) or a mix of i.m. for prime then i.n. for boosts, at 7-10 daysintervals. At day 42 post initial immunization, mice were challengedi.n. with 1.10⁵ PFU of a mouse adapted SARS-CoV-2 strain. Viral load inthe lungs was assessed at day 3 post infection.

FIG. 5A Immunization and challenge scheme.

FIG. 5B Neutralizing antibody titers against SARS-CoV-2 at day 42 postimmunization (prime-boost-boost), determined by plaque reductionneutralizing test (PRNT₅₀).

FIG. 5C Viral load (genomes copies as PFU equivalents) measured in thelungs at day 3 post challenge.

FIG. 5D Viral load (PFU per g of tissue) measure in the lungs at day 3post challenge.

FIG. 6 . ratio of IgG2a/IgG1 or Th1/Th2 responses.

The content of sera of Balb/c mice immunized with the receptor bindingdomain with the signal peptide of the spike (pVAX-RBD) using an i.m.prime-boost protocol were assessed by isotype specific ELISA against theSARS-CoV-2 RBD.

EXAMPLES Material and Methods

1. Design of the Antigens

Phylogenetic analysis of publicly available SARS-CoV-2 (2019-nCov)full-length sequences (NCBI sequence data base) with representativesequences for the genus Betacoronavirus indicates that SARS-CoV-2 ispart of a well-defined Sarbecovirus Glade that includes viruses sampledin bats (FIG. 1 ).

It is significantly different from the well-known human sarbecovirusSARS-Cov with only 79% identity at the nucleotide level over the fulllength of the genome. This value drops to 72.7% for S in nucleotides,and 76.2% in amino acids. However structural modelling using theSwiss-Model program (Waterhouse et al., Nucleic Acids Res., 2018 Jul. 2;46(W1): W296-W303) or Phyre2 (Kelley et al., Nat Protoc. 2015 June;10(6):845-58) and a representative sequence of the S protein of2019-nCov (SARS-CoV-2) as query suggest a similar structuralorganization to the S protein of SARS-Cov, with core sections showingstronger sequence or structure conservation and modeling quality, andvariation (with modelling uncertainty) mostly in the surface residues(FIG. 2 ).

In particular, a putative RBD of SARS-CoV-2 can be defined with, likefor SARS-Cov (SARS-CoV-1), a core and an external subdomain. As it hasbeen shown for other coronaviruses (Embemovirus MHV, HCov-229E orSARS-Cov), the RDB is highly reactive to anti-S neutralizing antibodies,and could comprise the key epitopes of the neutralizing response.

Based on the state of the art of betacoronaviruses biology, and inparticular building on the structural similarity with SARS-Cov, the Sprotein is the most relevant antigen to include regardless of thedelivery strategy. Two antigens have thus been designed (FIG. 3 ). Onecorresponds to the complete S protein, and the second, smaller (minimal)antigen, for ease of expression and production, correspond to theSARS-CoV-2 RBD of the S protein. To ensure secretion of the RBD antigen,3 signal peptides (SP) have been selected.

Specifically, antigen 1 consists of 1273 amino acids or 3822nucleotides, and the sequence has been codon-optimized for expression inHomo sapiens. Antigen 2 consists of 194 amino acids or 582 nucleotides,and the sequence has been codon-optimized for expression in Homosapiens. Antigen 2 is combined with one of 3 SP (from the SARS-CoV-2) Sprotein; from the human CD5 or from the human IL-2). Other versions ofAntigen 2 having SP variants according to the present disclosure arealso engineered, one with a SP lacking SA in positions 20-21 of SEQ IDNO: 23; one with a SP lacking RLVA in positions 25 to 28 of SEQ ID NO:19; and one with a SP lacking A in positions 20 of SEQ ID NO: 15.

These antigens can be delivered as nucleic acid immunogens, formulatedwith appropriate non-viral agent such as amphiphilic block copolymer orin a viral vector.

The antigens were also combined with a universal Pan HLA-DR Epitopetermed PADRE. PADRE is a universal synthetic 13 amino acid peptide thatactivates CD4+ T cells. As PADRE binds with high affinity to 15 of the16 most common human HLA-DR types, it provides potent CD4+ T cellresponses and may overcome problems caused by polymorphism of HLA-DRmolecules in human populations.

2. Plasmid Construction

The various cDNA sequences designed from 2019-nCov (SARS-CoV-2 or SARS2)sequences were codon-optimized for Homo sapiens expression, synthesized(Thermo-Fisher Scientific), and cloned into the pVAX-1 plasmid(Thermo-Fisher) under the control of a CMV promoter and containing aKozak sequence. The cDNA sequences correspond to SEQ ID NO: 10, 12, 14,16, 18, 20, 22, 24, 29, 31, 33, 35 in the attached sequence listing andencode r a protein antigen corresponding to the amino acid sequences SEQID NO: 11, 13, 15, 17, 19, 23, 25, 30, 32, 34 and 36, respectively inthe attached sequence listing. pVAX-Spike comprises the cDNA of SEQ IDNO: 10 encoding a Spike of SEQ ID NO: 11. VAX-Spike-deltaFurin comprisesthe cDNA of SEQ ID NO: 29 encoding a Spike-deltaFurin of SEQ ID NO: 30.pVAX-RBD comprises the cDNA of SEQ ID NO: 14 encoding a RBD of SEQ IDNO: 15. pVAX-RBD-PADRE comprises the cDNA of SEQ ID NO: 16 encoding aRBD-PADRE of SEQ ID NO: 17. All pVAX derived plasmids were amplified inEscherichia coli and plasmid DNA was purified on EndoFree plasmidpurification columns using the NucleoBond Xtra Maxi EF Kit (MachereyNagel). The constructs were verified by enzymatic digestion and bySANGER sequencing.

3. Formulation

The SARS-2 DNA vaccine is formulated by mixing equal volumes of ABCstock solution (Nanotaxi®, provided by In-Cell-Art; disclosed on page 13to 17 of WO 2019/092002) in water and plasmid DNA solution at thedesired concentration in 2× buffer solution, immediately prior tointramuscular injection. The mixing of ABC Nanotaxi® and plasmid DNA isa self-assembly process that results from hydrogen bonding, hydrophobic,and electrostatic interactions between ABC and DNA.

4. Antigen Expression/Western Blot Analysis

293 cells are transfected with plasmids expressing the antigens. After24h, cell lysates and supernatant are harvested. Samples arefractionated by SDS-PAGE and transferred to cellulose membranes to beprobed with anti-S antibodies or sera. A goat anti-mouse immunoglobulinG (IgG)-horseradish peroxidase (HRP) conjugate is used as secondaryantibody. Peroxidase activity is visualized with an enhancedchemiluminescence detection kit (Thermo Fisher Scientific).

5. Animal Vaccination

Animal experiments are performed according to institutional, French andEuropean ethical guidelines (Directive EEC 86/609/and Decree 87-848 of19 Oct. 1987) subsequent to approval by the Institut Pasteur Safety,Animal Care and Use Committee, protocol agreement delivered by the localethical committee and the Ministry of High Education and Research.Groups of at least 5 female Balb/c, transgenic K18-ACE2 (McCray et al.,J. Virol., 2007, 81(2), 813-821), or other mice type, including C57BL/6Cmice and interferon deficient mice such as IFNAR mice were housed underspecific pathogen-free conditions in individually ventilated cagesduring the immunization period at the Institut Pasteur animalfacilities. Mice were vaccinated with different constructs using aprime/boost regimen. Formulations was injected bilaterally into bothtibial anterior muscles using an 8-mm, 30-gauge syringe (intra muscular(i.m.)), or intra-nasally (i.n.) at different time intervals. Mice wereanesthetized by isoflurane before injection. A group of fiveunvaccinated mice, housed alongside the treated mice was used ascontrols. Sera were collected at various time points post-immunizationto monitor the immune responses.

6. Cell Culture

Vero C10008 clone E6 (CRL-1586, ATCC) cells were maintained inDulbecco's modified Eagle medium (DMEM) complemented with 10%heat-inactivated serum, 100 U/mL penicillin and 100 μg/mL streptomycinand were incubated at 37° C. and 5% CO2.

7. ELISA

Measurement of anti-S IgG antibody titers in serum of vaccinated mice isperformed using either a commercial kit or an in house assay.Recombinant SARS-CoV-2 RBD were coated on 96-well MAXISORP plates.Coated plates were incubated overnight at 4° C. The plates were washed 3times with PBS-0.05% Tween, then blocked 1 h at 37° C. with PBS-0.05%Tween-3% BSA. Serum samples from immunized mice were serially dilutedand incubated for 1 h at 37° C. on the plates. HRP-conjugatedisotype-specific (IgG1 or IgG2a) secondary antibodies were used toreveal the specific and relative amounts of IgG isotypes. Endpointtiters for each individual serum were calculated as the reciprocal ofthe last dilution giving twice the absorbance of the negative controlsera.

8. Plaque Reduction Neutralization Test (PRNT)

For plaque reduction neutralization titer (PRNT) assays, Vero-E6 cellsare seeded onto a 24-well plate and incubated at 37° C. for 12-24 h to90% confluency. Two-fold serial dilutions of heat-inactivated serumsamples are mixed with 50 PFU of SARS-CoV-2 for 1 h at 37 C, then addedto cells for 2 h at 37° C. Virus/serum mix are then aspirated, and cellswashed with PBS and overlaid with 1 mL of DMEM supplemented with with 5%fetal calf serum and and 1.5% carboxymethylcellulose. The plates wereincubated for 3 days at 37° C. with 5% CO2. Viruses were theninactivated and cells fixed and stained with a 30% crystal violetsolution containing 20% ethanol and 10% formaldehyde. Serum titer wasmeasured as the dilution that reduced SARS-CoV-2 plaques by 50% (PRNT50). This test was performed on several SARS-CoV-2 lineages as seen inthe circulation in human. The SARS-CoV-2 lineages included in particularGlade L, Glade G (GISAID) and lineages B.1.1.7 (UK variant), B.1.351(South Africa variant) and P.1 (Brazil variant).

9. SARS-CoV-2 Challenge

Animals were transferred to an isolator in BioSafety Level 3 animalfacilities of Institut Pasteur. Mice were anesthetized by intraperitoneal (i.p.) injection of a mixture of Ketamine and Xylazine,transferred into a biosafety cabinet 3 where they were inoculated i.n.with either 1.10⁵ PFU of a mouse adapted strain of SARS-CoV-2 (MaCo3)for wild type Balb/C mice or 1.10⁴ PFU of a low passage clinical isolate(BetaCoV/France/GES-1973/2020) for the transgenic K18-ACE2 mice. Theisolate BetaCoV/France/GES-1973/2020 was supplied by the NationalReference Centre for Respiratory Viruses hosted at Institut Pasteur(Paris, France) and headed by Pr. Sylvie van der Werf.

Three days after challenge, mice were sacrificed and lung samples werecollected aseptically, weighted, and mechanically homogenized inice-cold PBS. The presence of SARS-CoV-2 in the lung was detected bytitration on VeroE6 cells and by detecting viral RNA using a RT-qPCR(nCoV_IP4) targeting the RdRp gene, as described on the WHO website(https://www.who.int/docs/default-34source/coronaviruse/real-time-rt-pcr-assays-for-the-detection-of-sars-cov-2-institut-35pasteur-paris.pdf?sfvrsn=3662fcb6_2).

As SARS-CoV-2 infection is lethal for K18-ACE2 mice, symptoms andweights were monitored for 14 days after challenge.

10. Lung Histopathology

Samples from the lung were fixed in formalin for at least 7 days andembedded in paraffin for histopathological examination.

Results A prime-boost protocol with 4 weeks intervals betweenimmunizations was first used to evaluate the immunogenicity of thedifferent constructs. 100 μg of the pVAX plasmid containing either thecomplete SARS-CoV-2 spike, a spike modified at the furin site (spikedelta furin), only the receptor binding domain (RBD) with the nativesignal peptide of the spike or the RBD with the PADRE sequence in 3′(RBD-PADRE) was injected intra-muscularly (i.m.) The plasmid DNA wasmixed with an amphiphilic bloc copolymer for delivery.

The neutralizing potential of the sera was evaluated at day 27 (prior tothe second immunization), and 20 days later (FIG. 4A). Theneutralization plaque reduction neutralizing tests (PRNT₅₀) on thedifferent constructs revealed that the smallest antigen (RBD) with thenative signal peptide of the spike and without the PADRE sequenceresulted in an early response already detectable 4 weeks after the prime(FIG. 4B), and which was more homogenously and consistently boosted bythe second immunization in comparison to the other constructs (FIG. 4C).

Using the RBD construct, an accelerated protocol of a prime with twoboosts, administered at 7-10 days intervals was next used (FIG. 5A). Atday 42, the neutralizing potential of sera elicited using i.m, intranasal (i.n.) and a mix of i.m. prime followed by boosts using the i.n.route was compared.

However, the challenge with a mouse adapted strain of SARS-CoV-2inoculated i.n. revealed that the mixed protocol of i.m. and i.n.resulted in a lower viral load in the lungs of the animals in terms ofviral RNA copies (FIG. 5C) and no infectious particles could be detectedby titration. As expected from the PRNT results, mice immunized only bythe i.n. route presented viral loads comparable to the mock vaccinated(empty vector pVAX) group (FIG. 5D). This shows that an acceleratedimmunization scheme over a short period of time can lead to strongneutralizing antibody titers.

As IgG isotype switching can serve as indirect indicators of Th1 and Th2responses, the SARS-CoV-2 RBD-specific IgG1 and IgG2a isotype titerswere determined in the sera of Balc/c mice immunized with the RBDantigen. Significantly higher IgG2a antibody titers than IgG1 wereobserved, reflecting a predominant Th1-type immune response (FIG. 6 ).

In conclusion, this study indicates that the RBD antigen is able toprovide protection from a SARS-CoV-2 challenge of immunized animals,correlating with strong neutralizing antibody induction.

1. A DNA construct encoding a SARS-CoV-2 virus Spike (S) protein antigencomprising a signal peptide comprising the amino acid sequence of SEQ IDNO:5, wherein said DNA construct comprises a receptor binding domain(RBD) sequence having at least 90% identity with nucleotides 1-582 ofSEQ ID NO:3, and wherein said DNA construct comprises a Kozak sequencecomprising the sequence CACC in positions −4 to −1 relative to the ATGinitiation codon of the S protein antigen.
 2. The DNA construct of claim1, wherein the S protein antigen comprises an amino acid sequence havingat least 90% identity with SEQ ID NO:
 4. 3. The DNA construct of claim1, wherein the S protein antigen has at least 95% identity with theamino acid sequence from positions 19 to 1273 of SEQ ID NO:2.
 4. The DNAconstruct of claim 1, wherein the S protein antigen has at least 97%identity with the amino acid sequence from positions 19 to 1273 of SEQID NO:2.
 5. The DNA construct of claim 1, wherein the S protein antigenhas at least 99% identity with the amino acid sequence from positions 19to 1273 of SEQ ID NO:2.
 6. The DNA construct of claim 1, wherein the Sprotein antigen has 100% identity with the amino acid sequence frompositions 19 to 1273 of SEQ ID NO:2.
 7. (canceled)
 8. (canceled)
 9. TheDNA construct of claim 1, wherein said DNA construct comprises a Kozaksequence comprising the sequence GCCACC in positions −6 to −1 relativeto the ATG initiation codon of the S protein antigen.
 10. The DNAconstruct of claim 1, wherein said DNA construct comprises an RBDsequence consisting of nucleotides 1-582 of SEQ ID NO:3.
 11. The DNAconstruct of claim 1, wherein said DNA construct comprises an RBDsequence having at least 91% identity with nucleotides 1-582 of SEQ IDNO:3.
 12. The DNA construct of claim 1, wherein said DNA constructcomprises an RBD sequence having at least 93% identity with nucleotides1-582 of SEQ ID NO:3.
 13. The DNA construct of claim 1, wherein said DNAconstruct comprises an RBD sequence having at least 95% identity withnucleotides 1-582 of SEQ ID NO:3.
 14. The DNA construct of claim 1,wherein said DNA construct comprises an RBD sequence having at least 97%identity with nucleotides 1-582 of SEQ ID NO:3.
 15. The DNA construct ofclaim 1, wherein said DNA construct comprises an RBD sequence having atleast 98% identity with nucleotides 1-582 of SEQ ID NO:3.
 16. The DNAconstruct of claim 1, wherein said DNA construct comprises an RBDsequence having at least 99% identity with nucleotides 1-582 of SEQ IDNO:3.
 17. The DNA construct of claim 9, wherein said DNA constructcomprises an RBD sequence having at least 91% identity with nucleotides1-582 of SEQ ID NO:3.
 18. The DNA construct of claim 9, wherein said DNAconstruct comprises an RBD sequence having at least 93% identity withnucleotides 1-582 of SEQ ID NO:3.
 19. The DNA construct of claim 9,wherein said DNA construct comprises an RBD sequence having at least 95%identity with nucleotides 1-582 of SEQ ID NO:3.
 20. The DNA construct ofclaim 9, wherein said DNA construct comprises an RBD sequence having atleast 97% identity with nucleotides 1-582 of SEQ ID NO:3.
 21. The DNAconstruct of claim 9, wherein said DNA construct comprises an RBDsequence having at least 98% identity with nucleotides 1-582 of SEQ IDNO:3.
 22. The DNA construct of claim 9, wherein said DNA constructcomprises an RBD sequence having at least 99% identity with nucleotides1-582 of SEQ ID NO:3.